The downgrade may be a personal humiliation for Mr Osborne, but the lack of
politically and economically viable alternatives make calls for a change of
Chancellor and course look hollow.

It is possible to date the beginnings of Nicolas Sarkozy's political demise almost exactly to the loss of France's triple–A credit rating.

Like George Osborne, the then French president had set much store by its defence; to lose this stamp of economic approval was a humiliating personal blow from which he never fully recovered.

Does the same fate now await Mr Osborne, who has similarly trumpeted the triple–A as validation of his strategy – and, by extension, David Cameron , who in some respects has been even more vocal in flaunting this symbol of economic virility?

Politically, there is no doubt that this is a big deal, though almost certainly not in the same league as the Major government's exit from the ERM, an event that shattered the Tories' reputation for economic competence.

One of the Coalition's early triumphs was to claw back the triple–A from almost certain loss under Labour with an "emergency Budget", which outlined what then seemed a decisive plan for dealing with the deficit.

Yet lack of growth has derailed the strategy, pushing the date at which the structural deficit is eliminated well into the next parliament. This has led to growing calls from both Left and Right for a change in course – for fiscal stimulus from the Left, and for tax cuts from the Right.

The downgrade makes no such demands. Moody's, the agency responsible, goes out of its way to say that the Government is essentially on the right course. Indeed, it strongly implies that to embark on the sort of stimulus suggested by Labour would lead to further downgrades.

In this sense, loss of the triple–A only further underlines just how little room the Chancellor has in next month's Budget for any easing of the broad outline of fiscal consolidation.

The downgrade may be a personal humiliation for Mr Osborne, but the lack of politically and economically viable alternatives make calls for a change of Chancellor and course look hollow. And while the decision by Moody's will add to the pressure on the pound, in other respects it will have few immediate economic consequences.

The examples of Japan and the USA show that ratings downgrades have little or no impact on interest rates for countries that can borrow in their own currency.